The present invention relates to photoresist compositions, particularly those well suitable for etching a polyimide layer forming a protective layer of a flexible printed wiring board. The present invention also relates to flexible printed wiring boards having a protective layer consisting of a polyimide layer formed with said photoresist compositions.
Flexible wiring boards having a protective layer on the conductive circuit have previously been widely known. This protective layer serves to protect the conductive circuit and to provide an insulating coating for the conductive circuit, and has commonly been formed by applying a polyimide film having an adhesive layer called as an adhesive-backed polyimide film on the conductive circuit.
The polyimide film has been punched to expose terminal parts of the conductive circuit or to apply the polyimide film to an intended location.
We previously proposed a preparation process described in JPA No. 18114/97 to solve the problems associated with punching of the polyimide film, such as punching accuracy or die costs and insufficient film strength of the punched polyimide film for continuous production.
This preparation process succeeded in achieving the initial purpose of providing a flexible wiring board without need of punching the polyimide film, by forming a laminate of a polyimide precursor layer and a photoresist layer on a copper foil (using a composite film of a polyimide precursor layer and a photoresist layer laminated to each other in the examples), patterning said laminate via exposure and development, and etching the polyimide precursor layer through the patterned photoresist layer as a mask.
However, some problems remain outstanding. Namely, a problem lies in that the photoresist layer is separated from the polyimide precursor layer under the action of the etching solution (alkaline developing solution) to fail in sufficiently protecting the polyimide precursor layer when the etching period is extended in accordance with the thickness of the polyimide precursor layer or the constituent materials of the polyimide precursor layer.
Another problem lies in that the pattern width tends to be narrower than intended during patterning of the photoresist layer, and the width of the polyimide precursor layer also becomes narrower than intended along said pattern width during the subsequent etching of the polyimide precursor layer.
Thus, any prior art has not entered into photoresist materials through which the polyimide precursor layer is etched and further improvement has been demanded.
In order to solve the above problems, the first object of the present invention is to provide a photoresist composition which prevents separation of the photoresist layer formed on a polyimide precursor layer during etching.
The second object of the present invention is to provide a photoresist composition, which can improve patterning accuracy during patterning of the photoresist layer. The third object of the present invention is to provide a flexible wiring board having a protective layer obtained by etching a polyimide precursor layer using a photoresist composition fulfilling the first and second objects.
Thus, the invention of the present application relates to a photoresist composition for etching a polyimide precursor layer on a conductive circuit, comprising a photopolymerizable organic material (A) (including either one or both or a composition of photopolymerizable oligomer and photopolymerizable monomer; hereinafter the same in this invention), a water-soluble resin (B) and an amino-group-containing resin (C).
The invention relates to a photoresist composition for etching a polyimide precursor layer on a conductive circuit, comprising a photopolymerizable organic material (A), a water-soluble resin (B) and an amino-group-containing resin (C), wherein the water-soluble resin (B) includes either one or both of a water-soluble nylon and an alcohol-soluble nylon.
The invention relates to a photoresist composition for etching a polyimide precursor layer on a conductive circuit, comprising a photopolymerizable organic material (A) and a water-soluble resin (B), and further comprising an amino-group-containing resin (C) in the range from 0.5 parts by weight to 6.0 parts by weight both inclusive based on 100 parts by weight of the total weight of the photopolymerizable organic material (A) and the water-soluble resin (B).
The invention relates to a photoresist composition for etching a polyimide precursor layer on a conductive circuit, comprising a photopolymerizable organic material (A) and a water-soluble resin (B) including either one or both of a water-soluble nylon and an alcohol-soluble nylon, and further comprising an amino-group-containing resin (C) in the range from 0.5 parts by weight to 6.0 parts by weight both inclusive based on 100 parts by weight of the total weight of the photopolymerizable organic material (A) and the water-soluble resin (B).
Above mentioned photoresist composition wherein the amino-group containing resin (C)is acrylic resin.
The invention relates to a flexible printed wiring board having a conductive circuit and a polyimide precursor layer on the conductive circuit, wherein the polyimide precursor layer has a pattern obtained by the steps of applying a photoresist composition comprising a photopolymerizable organic material (A), a water-soluble resin (B) and an amino-group-containing resin (C) on the surface of the polyimide precursor layer to form a photoresist layer, then patterning the photoresist layer and transferring the pattern of the photoresist layer to the polyimide precursor layer by etching.
The invention relates to a flexible printed wiring board, wherein the polyimide precursor layer is imidated after the pattern of the photoresist layer has been transferred thereto.
The invention relates to a flexible printed wiring board, wherein the water-soluble resin (B) includes either one or both of a water-soluble nylon and an alcohol-soluble nylon.
The invention relates to a flexible printed wiring board, which comprises an amino-group-containing resin (C) in the range from 0.5 parts by weight to 6.0 parts by weight both inclusive based on 100 parts by weight of the total weight of the photopolymerizable organic material (A) and the water-soluble resin (B).
The invention relates to a flexible printed wiring board having a conductive circuit and a polyimide precursor layer on the conductive circuit, wherein the polyimide precursor layer has a pattern obtained by the steps of applying a photoresist layer formed from a photoresist composition comprising a photopolymerizable organic material (A), a water-soluble resin (B) and an amino-group-containing resin (C) on the surface of the polyimide precursor layer, then patterning the photoresist layer and transferring the pattern of the photoresist layer to the polyimide precursor layer by etching.
The invention relates to a flexible printed wiring board, wherein the polyimide precursor layer is imidated after the pattern of the photoresist layer has been transferred.
The invention relates to a flexible printed wiring board, wherein the water-soluble resin (B) includes either one or both of a water-soluble nylon and an alcohol-soluble nylon.
The invention relates to a flexible printed wiring board, which comprises an amino-group-containing resin (C) in the range from 0.5 parts by weight to 6.0 parts by weight both inclusive based on 100 parts by weight of the total weight of the photopolymerizable organic material (A) and the water-soluble resin (B).
Above mentioned flexible printed wiring board wherein the amino-group-containing resin (C) is acrylic resin.
We attempted to enhance adhesion between the polyimide precursor layer and the photoresist layer in order to attain the objects of the present invention.
Thus, the polyimide precursor layer consists of a polyamic acid containing an acid anhydride and an aromatic diamine, and the acid anhydride has both of a carboxylate group attached to an amine and a carboxylate group unattached to an amine.
Having paid attention to the carboxylate group unattached to an amine in the polyimide precursor layer, we found that adhesion is improved by incorporating the resin (C) containing an amino group into the photoresist layer to react the carboxylate group in the polyimide precursor layer and the amino group in the photoresist layer or to allow the carboxylate group in the polyimide precursor layer and the amino group in the photoresist layer to be strongly attracted to each other, and thus accomplished the present invention.
We also conceived of incorporating a monomer containing an amino group into the photopolymerizable organic material (A), but we did not choose it because such a monomer tends to evaporate immediately after application of a photoresist composition on the polyimide precursor layer due to its low boiling point and accordingly can not help to stably enhance adhesion to the polyimide precursor layer.
When the water-soluble resin (B) is a water-soluble nylon and/or an alcohol-soluble nylon of this invention, etching resistance of the photoresist layer can be enhanced to further prevent separation of the photoresist layer.
When the content of the amino-group-containing resin (C) in the photoresist composition is within a specific range of this invention, patterning accuracy of the photoresist layer can be improved.